Once-through steam generator having a pair of tube bundles of spiral tube construction



N. D. ROMANOS Aug. 29, 1967 BUNDLES OF SPIRAL TUBE CONSTRUCTION 5 Sheets-Sheet 1 Filed May 24, 1965 INVENTOR NICHOLAS D. ROMANOS FIG.

Aug. 29, 1967 RQMANQS 3,338,301

ONCE-THROUGH STEAM GENERATOR HAVING A PAIR OF TUBE BUNDLES OF SPIRAL TUBE CONSTRUCTION Filed May 24, 1965 5 Sheets-Sheet 2 INVENTOR NICHOLAS D. ROMANOS ATTORNEY 3,338,301 TUBE N. D. ROMANOS UGH STEAM GENERATOR HAVING A PAIR OF BUNDLES OF SPIRAL TUBE CONSTRUCTION Aug. 29, 1967 ONCE-THRO Filed May 24, 1965 INVENTOR NICHOLAS D. ROMANOS BY M ATTORNEY United States Patent 3,338,301 ONCE-THROUGH STEAM GENERATOR HAVING A PAIR OF TUBE BUNDLES 0F SPIRAL TUBE CONSTRUCTION Nicholas D. Romanos, Chattanooga, Tenn., assignor to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed May 24, 1965, Ser. No. 458,059 7 Claims. (Cl. 165-145) The present invention relates generally to vapor generators employing gas as a heating medium. More particularly, the invention relates to a gas-operated vapor generator having an internal construction that provides for the utilization of a large number of heat exchange tubes and a minimum amount of containment space wherein the tubes are arranged for substantially uniform heat absorption and the containment structure is protected against excessive thermal stresses.

One of the sources of heat made available for the generation of vapor is the gas employed as a coolant for reaction processes. The utilization of this heat source for vapor generation purposes has been somewhat retarded due to the lack of apparatus that is capable of effectively utilizing gas as its heating medium. The paucity of effective gas-operated vapor generators comes about as a result of the great size and weight of a unit necessary to operate with this heating medium. Design concepts proposed to reduce the size of high capacity gas-operated vapor generators are undesirable for most purposes due to their interposing of serious problems into the operation of the unit. First of all, the use of a large number of heat exchange tubes in a minimum amount of space has a tendency to create overcrowding conditions within the containment vessel. Such overcrowding is undesirable because it has a deleterious effect upon the flow of fluid through the vessel by increasing the amount of pressure necessary to produce such fluid flow. Secondly, it is un desirable in that overcrowding of tubes impedes and oftentimes even prevents effective inspection and service of the tubes due to their inacessibility. And thirdly, a reduction in size and weight of the vessel employed to house high capacity heat transfer apparatus gives rise to the possibility of the induction of excessive thermal stresses within the shell because of the experiencing of undue thermal gradients by the shell.

By means of the present inventon there is provided a vapor generating apparatus that is compact in form, operationally eflicient and free from the above-cited defects. The arrangement of heat exchange surface within the unit is such as will provide the greatest amount of heating surface Within a minimum amount of space Without the creation of overcrowded tube conditions within the unit. The herein disclosed unit provides an arrangement of tubes within the containment vessel such that easly access to the vessel interior and the tube bundle can be had for the purpose of tube inspection and maintenance. Moreover, the terminal ends of the tubes are conveniently located at one end of the vessel such that unimpeded access can be had thereto for the purpose of inspecting the tube ends and plugging damaged tubes where necessary.

Another important feature of the invention provides for the flow of heating fluid through the unit in such a manner that the thermal gradients experienced by the unit components are minimized, thereby preventing undue thermal stresses within these components.

The objects and advantages of the present invention will appear from the following description of one embodiment thereof, and the novel features will be particu- 3,3383% Patented Aug. 29, 1967 larly pointed out hereinafter in connection with the appended claims.

The invention is described with reference to the accompanying drawings wherein:

FIGURE 1 is a diagrammatic elevation view of apparatus employing the problems of the invention;

FIGURE 2 is a sectional elevation of the vapor generator portion of the unit shown in FIGURE 1;

FIGURE 3 is a bottom view of the vapor generator;

FIGURE 4 is a cross-sectional view taken along line 44 of FIGURE 2;

FIGURE 5 illustrates in greater detail the tube support structure employed in the present invention; and

FIGURE 6 is a sectional elevation illustrating the tubular interconnection between corresponding tubes of the tube bundles.

With reference to the drawings, there is shown in FIG- URE 1 aform of the vapor generator apparatus contemplated by the present invention. It comprises a reaction vessel 10 that employs gas as a medium for cooling the vessel during the reaction process. The vessel 10 has its wall 12, which surrounds the operating parts indicated generally as 14, open at the bottom for the direct attachment of the vapor generator apparatus 16 that employs the reaction coolant gas as its heating medium. A circulating pump 18 is attached to continuously circulate the gas between the reaction vessel 10 and vapor generator 16.

As shown in FIGURE 2, the vapor generator 16 comprises a vertically arranged cylindrical shell 20 that is open at its top end and directly connected to the lower end of the vessel Wall by means of a conical transition member 22 welded to the two ends. The lower end of the vapor generator 16 is closed by a generally dish-shaped closure cover 24 by means of threaded connectors 26 that are cir cumferentially spaced about mating flanges 28 and 30 on the respective members. The herein shown circulating pump 18 is of the close-coupled type and attaches to the shell 20 by means of a cylindrical contact 32 that penetrates the wall of the shell to establish communication with the vapor generator interior.

Within the vapor generator shell 20 are positioned a pair of axially aligned tube bundles 34 and 36 that are generally annular in shape. Each of the tube bundles 34 and 36 comprises a plurality of vertically spaced layers of spirally wound heat exchange tubes 38 that are adapted to conduct a vaporizable fluid such as water. As shown in FIGURE 5, formed metal strips 40 are disposed between adjacent tube layers to form the tube support structure. The tubes in each adjacent layer are ofiset by approximately one-half the tube space to form a triangular pitch tube grid for better heat transfer characteristics and for the utilization of the tube material for means of vertical radiation shielding in the disclosed embodiment. Each tube bundle 34 and 36 consists of forty-four tube layers, each containing eight intermeshed tube coils with each tube coil representing approximately 1% turns. Each tube 38 in the upper tube bundle 34 connects with a corresponding tube in the lower tube bundle to give rise to a vapor generator unit containing 352 independent once-through flow circuits that present approximately 8,000 sq. ft. of heating surface. It is to be understood that the above figures are given by way of example only, and that greater or less numbers of fluid circuits or the number of layers in each tube bundle can be employed without departing from the scope of the invention.

The connection of corresponding tube coils 38 in each tube bundle is effected by means, as illustrated in FIG- URE 6, of vertical tubular connectors 42 that are disposed about the outer periphery of the tube bundles 34 and 36 and which attach to the outer terminal ends of their respective coils. As shown in FIGURE 4, by angularly offsetting the outer terminal ends of the tube coils in each layer 45 an arrangement can be obtained whereby the tubular connectors 42 are caused to surround the tube bundles on slightly greater than 1 spacing.

The inner terminal ends of the tubes 38 comprise the fluid inlets to the lower tube bundle 36 and the outlets of the tubes in the upper tube bundle 34. As shown in the drawings, the ends of these tubes are connected to appropriate inlet and outlet, tube manifolds 44 and 46 in the closure head 24 by means of inlet connectors 48 that extend between the inlet ends of the coils 38 in the lower tube bundle 36 and the inlet manifold 44 and outlet connectors 50 that extend between the outlet ends of the tubes in tube bundle 34 and the outlet manifold 46. The connectors 48 and 50 are arranged in clusters or groups as shown best in FIGURE 4 with each manifold receiving an equal number thereof. In the disclosed embodiment the inlet connectors 48 emanate from four inlet manifolds 44 that are disposed on 90 spacing about one diameter of the closure head 24 while the outlet connectors 50 connect with four outlet manifolds similarly disposed about another diameter of the closure head and offset by 45 from the inlet manifolds. The manifolds 44 and 46 each comprise a cylindrical sleeve 52 that is attached to the head 24 about spaced openings that permit passage of the tubular connectors. The outer end of the sleeve 52 is closed by a tube sheet 54 in which are provided a number of tube seats for attaching the ends of the connectors 48 and 50. A dome-shaped tube 56 having a nozzle 58 and an accessway 60 overlies each tube sheet 54, thereby forming inlet chambers 62 or outlet chambers 64 in the respective manifolds.

Bafliing within the vapor generator directs coolant gas from the reaction vessel along the axis of the unit from whence it flows in heat exchange relation with the fluid flowing in the tubular coils 38 radially outwardly through the tube layers in the upper tube bundle 34, then inwardly through the tube layers in the lower tube bundle 36 and on to the recirculating pump 18 whereby it is returned to the reaction vessel 10. The baffling arrangement employed comprises an elongated cylindrical enclosure plate 66 that is disposed in co-axial relation with the tube bundles 34 and 36 and spaced from the wall of the vapor generator shell 20. Upper and lower lateral baffle plates 68 and 70 having central openings 72 and 74 attach to the ends of the cylindrical plate 66 to form with the latter an enclosure for the tube bundles 34 and 36. A median lateral divider 76 is interposed between the tube bundles 34 and 36 and divides the tube bundle envelope into two chambers 35 and 37. The outer peripheral edge of divider 76 is spaced from the wall of the cylindrical plate 66 to permit the flow of gas from the upper tube bundle chamber 35 to the lower chamber 37. Circu-mf-erentially spaced openings 78 are provided in the plate 76 to permit passage of the clusters of outlet connectors 50 to the outlet manifolds 64. Cylindrical thermal sleeves 80 surround the clusters between the openings 78 and manifolds 46 thereby insulating the connectors from the cooler gas flowing in this region. A conical baffle plate 82 attaches between the central opening 72 in plate 68 and the central passage through the operating parts 14 of the reaction vessel 10 to direct gas from the vessel to the upper tube bundle chamber 35.

Surrounding the cylindrical enclosure plate 66 is a second cylindrical plate 84 which is disposed in co-axial relation with, and between, the plate 66 and the wall of the shell 20. The plate 84 is fitted as by means of an interference fit at its upper end to the outer surface of the plate 66 and is attached at its lower end to the inner face of flange 30, thereby forming a first annular gas pass 86 that is in communication with the discharge end of the lower chamber 37 and is effective to conduct spent gas to the circulating pump 18. Communication of the first gas pass 86 with pump 18 is effected by means of a conduit 88 that connects with the wall of the cylindrical plate 84 4 and is concentrically disposed within conduit 32 to form an axial pump inlet passage 90 and an outer annular pump outlet passage 92. As shown in FIGURE 2, the pump outlet passage 92 communicates with a second annular gas pass 94 formed between the wall of shell 20 and the second cylindrical baflde plate 84. The second gas pass 94 is caused to communicate with the reaction vessel 10 and is utilized for the return of spent coolant gas from the vapor generator 16 to the vessel 10.

In operation, gas that is employed for cooling the reaction process occurring Within the vessel 10 is caused to flow in heat exchange relation with vaporizable fluid that enters the tube coils 38 through the inlet manifolds 44. The gas is directed into the upper tube bundle chamber by means of baffle 82 from whence it flows radially outwardly through the tube coils in tube bundle 34 and thereafter inwardly through the tube coils in the lower tube bundle 36 in chamber 37. The gas leaves the envelope through the central opening 74 and flows around the annular passage 86 to the circulating pump inlet passage 96 from whence it is discharged through passages 92 and 94 back to the reaction vessel 10. The vaporizable liquid supplied to the tube coils 38 through inlet manifold 44 is heated in the coils to produce high pressure vapor. The degree of heat exchange existing within the vapor generator may be such as will produce high pressure vapor in the lower tube bundle 36 followed by superheating to an elevated temperature in the upper tube bundle 34. On the other hand, the exchange of heat within the vapor generator can, if desired, be regulated such that vapor is created in the upper tube bundle with the vapor emerging from outlet manifold 64 containing little or no superheat.

By means of the invention there is provided a high capacity vapor generator wherein the amount of vapor generated in each fluid circuit is substantially the same and wherein access of the tubes is greatly facilitated. Because of the fact that the terminal ends of all of the tubes are disposed at one end of the vapor generator shell, access to the tube ends can be easily obtained through accessways 60 for the purpose of inspecting and/ or servicing the tube ends. Moreover, access to the tube bundles and other internal structure of the unit can readily be obtained by the removal of the closure head 24 and with it, the tube coils 34 and 36 and bafiie elements 66 through 82.

Because of the arrangement of the internal structure of the vapor generator the component parts of the unit are protected against undue thermal stresses. The wall of the shell 20 is protected against excessive temperatures due to the fact that only cool, spent gas is permitted to contact the wall. Similarly, the envelope forming cylindrical plate 66 is protected against thermal stresses due to thermal gradients along its length because of the fact that the temperature of the gas that comes in contact with the plate is substantially the same throughout the length of the plate.

What is claimed is:

1. A vapor generator comprising (a) a cylindrical shell adapted at one end for attachment to a source of heating fluid, said shell having concentrically related heating fluid inlet and outlet openings at said one end,

(b) closure means closing the other end of said shell,

(c) a pair of axially spaced annular tube bundles, each including axially spaced layers of coiled heat exchange tubes, housed within said shell,

((1) means for connecting corresponding tubes in said tube bundles for series flow,

(e) sai-d tubes having terminal ends arranged in groups and disposed adjacent and enclosed by the inner periphery of said tube bundles,

(f) a plurality of vaporizable fluid manifold means spacedly disposed about said closure means for passing vaporizable fluid through said tubes,

(g) means for attaching said tube ends to said manifold means including tubular extensions extending substantially parallel to the axis of said shell cOnnecting between said tube ends and said manifold means,

(h) baflle means for directing the flow of heating fluid through said shell including (i) cylindrical plate means spaced from the wall of said shell forming an interior tube bundle chamber enclosing said tube bundles and an exterior heating fluid flow passage,

(ii) said cylindrical plate means including end plates disposed at the ends of said chamber having central openings for axial flow of heating fluid into and out of said chamber,

(iii) a laterally disposed partition plate positioned intermediate said tube bundles dividing said tube bundle chamber into compartments, said plate having its peripheral edge spaced from the wall of said chamber to form an annular opening connecting said compartments for the passage of heating fluid substantially radially through each of said tube bundles,

(j) and means for passing heating fluid from said heating fluid inlet opening, through said tube bundle chamber and back through said heating fluid flow passage to said outlet opening.

2. Apparatus as recited in claim 1 wherein said tubular extensions are arranged in groups and said partition plate includes means forming openings for passing groups of tubular extensions connecting the ends of tubes in the tube bundle remote from the closed end of said shell.

3. Apparatus as recited in claim 2 including thermal sleeves connected between said partition plate and said manifold means and enclosing the tubular extensions connecting the ends of tubes in the tube bundle remote from the closed end of said shell.

4. Apparatus as recited in claim 3 including (a) axially elongated cylindrical baflie concentrically disposed between said plate means and said shell Wall dividing said heating fluid flow passage into concentric first and second passes,

(b) means connecting said first pass and the outlet end of said tube bundle chamber,

(c) means connecting said second pass and the outlet of said shell,

(d) and pump means operatively connected between said first and second passes for circulating heating fluid through said vapor generator.

5. Apparatus as recited in claim 4 including (a) first conduit means connecting the inlet of said pump means to said first pass,

(b) and second conduit means concentrically related to said first conduit means connecting the discharge of said pump means to said second pass.

6. Apparatus as recited in claim 3 wherein said tube bundles comprise axially spaced layers of spirally wound heat exchange tubes.

7. Apparatus as recited in claim 6 wherein said axially spaced layers in each tube bundle comprise a plurality of concurrent, spirally wound heat exchange tubes having one end disposed within the inner periphery of said layers for connection with said extensions and their other end disposed adjacent the outer periphery of said layers for connection with corresponding tubes in the other tube bundle.

References Cited UNITED STATES PATENTS 896,339 5/ 1962 Great Britain.

MEYER PERLIN, Primary Examiner. A. W. DAVIS, Assistant Examiner. 

